Clinical Research Directory

Inclusion Criteria: * Age\> 5 years and \< 55 years * Childhood or juvenile/adult onset * Residing in the Netherlands * Current ERT with alglucosidase alfa\> 2 years (dose regimen 20 or 40 mg/kg bi-weekly). * Confirmed diagnosis: enzyme deficiency in any tissue source and/or 2 confirmed disease-causing variants in the GAA gene. * Willing and able to adhere to study procedures * Deterioration in pulmonary function and/or 6MWT and/or muscle strength despite current treatment regimen with alglucosidase alfa. * Disease status: measurable pulmonary (dys)function: (F)VC ≤ 80% predicted (mechanic ventilation during the day or night allowed); Measurable muscle weakness in proximal and/or distal muscle groups (non- ambulant/wheelchair bound patients allowed); measurable functional ability Exclusion Criteria: * Age\>55 years * Invasive mechanical ventilation * No remaining useful functional ability, as decided by the treating physician * Unmanageable, sever IAR's on alglucosidase alfa * Deterioration due to high levels of anti-alglucosidase alfa antibodies interfering with treatment efficacy * Female patient of childbearing potential not protected by highly effective contraceptive method of birth control and/or who is unwilling or unable to be tested for pregnancy